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Aims: Basal cell carcinoma (BCC) is a common cancer, with a high risk of local recurrence. A quantifiable measurement of the histological margins of BCC in excisions is a recurrent demand of clinicians; however, there are currently no international guidelines indicating its value. Methods and results: A questionnaire validated by four experts in dermatopathology and formatted under a 'Google Forms'‐type interface was sent by e‐mail to physicians specializing in surgical pathology or dermatopathology and practising in France from 20 March 2018 to 20 May 2018. The results were compared between subgroups according to age and subspecialisation, especially dermatopathology. The questionnaire was completed by 225 practitioners. Microscopic margins were systematically measured in 77.3% of cases, sometimes in 19.6% and never in 3.1%. The main reason was to report factually insufficient margins (66.5%), followed by laboratory routine (45%) or clinician requests (43.1%). For 72% of respondents, the clinical or histopathological criteria did not influence their practice. The most used tool was a graduated ruler placed under a microscope (44.3% of cases). Compared to other groups, dermatopathologists measured BCC margins less systematically [only in certain situations (33.3 versus 14.9%) or never (10.5 versus 0.6%) (P < 0.001)] and used an eyepiece reticle more extensively (53.1 versus 29.8%; P = 0.0029). Conclusion: The measurement of histological margins in BCC is common practice in France, although there are no recommendations. Our survey suggests that it represents a way for pathologists to specify an insufficient margin and therefore the need for scar revision. [ABSTRACT FROM AUTHOR]

To prospectively assess the impact of expert pathological review of skin adnexal carcinoma diagnosis in France. From 2014 to 2019, 2573 samples from patients with newly diagnosed or suspected skin adnexal carcinomas were reviewed prospectively by expert pathologists through the national CARADERM (CAncers RAres DERMatologiques) network. Changes in diagnosis between referral and expert review were analysed regarding their potential impact on patient care or prognosis. The samples comprised 2205 newly diagnosed adnexal carcinomas, 129 benign adnexal tumours, 136 basal cell carcinomas, 74 squamous cell carcinomas, six cutaneous metastases and 13 other malignancies. There were 930 (42%) sweat gland carcinomas, of which porocarcinoma (261; 11.8%), microcystic adnexal carcinoma (125; 5.7%) and hidradenocarcinoma (109; 4.9%) were the most frequent subtypes; 778 (35%) hair follicle carcinomas, 238 (11%) sebaceous carcinomas and 212 (10%) extramammary Paget diseases/mammary-like anogenital gland adenocarcinomas. A diagnostic change between referral and expert review occurred in 503 (21.3%) patients, significantly higher for cases sent with a provisional diagnosis seeking an expert second opinion (45.7%) than for cases sent with a formal diagnosis (2.8%) (p <.0001). Sweat gland carcinomas were more prone to diagnostic discrepancies than other tumours (p <.0001), including 1.8% of patients with sweat gland carcinoma subtype misclassification with predicted clinical impact. Changes between benign and malignant conditions occurred in 117 samples (5% of patients). The study provides a unique description of the distribution of skin adnexal carcinomas and highlights the importance of expert review for these rare cancers. Optimal clinical management was impacted in a significant proportion of patients. • nationwide prospective study on 2205 skin adnexal carcinomas with pathological review. • sweat gland carcinoma, 35% hair follicle carcinoma and 11% sebaceous carcinoma. • Diagnostic change in 21.3% of samples after expert pathological review. • Sweat gland carcinomas more prone to diagnostic discrepancies. • 8.6% of patients with diagnostic change predicted to impact patient management. [ABSTRACT FROM AUTHOR]